1. Field of the Invention
The present invention relates to a multi-cylinder reciprocating compressor, and more particularly, to a multi-cylinder reciprocating compressor suited for use in an automotive air conditioning system.
2. Description of the Related Art
An air conditioning system for a motor vehicle comprises a refrigeration circuit which includes, for example, a multi-cylinder reciprocating compressor. The reciprocating compressor is disposed between an evaporator and a condenser in the refrigeration circuit and has a plurality of pistons fitted in a cylinder block thereof. The pistons are reciprocated in turn by rotation of a swash plate. As the pistons reciprocate, the reciprocating compressor sucks in a refrigerant, compresses the refrigerant into a high-pressure state, and discharges the high-pressure refrigerant to the condenser.
More specifically, the reciprocating compressor has a refrigerant suction chamber and a refrigerant discharge chamber. The suction and discharge chambers are defined inside the cylinder head of the compressor. As is clear from U.S. Pat. No. 6,293,763, the discharge chamber is located at the center of the cylinder head and connected to the condenser through a discharge port. The suction chamber is an annular chamber surrounding the discharge chamber and is connected to the evaporator through a suction port. During the suction stroke of a piston, a compression chamber associated with the piston is connected to the suction chamber through a suction valve, so that the refrigerant is introduced into the compression chamber from the suction chamber. In the last stage of the subsequent compression/discharge stroke of the piston, the compression chamber is connected to the discharge chamber through a discharge valve, and therefore, the high-pressure refrigerant is discharged from the compression chamber to the discharge chamber.
In the multi-cylinder reciprocating compressor described above, the pistons, that is, the compression chambers, are arranged at intervals in the circumferential direction of the swash plate. Accordingly, as the swash plate rotates, the refrigerant in the suction chamber is introduced sequentially into the compression chambers. When the refrigerant is introduced into each compression chamber, the pressure in the suction chamber temporarily drops, and the pressure drop allows the refrigerant to flow into the suction chamber through the suction port, so that the pressure in the suction chamber rises.
Thus, each time the refrigerant is introduced into each compression chamber, the pressure in the suction chamber rises and falls. Since the suction chamber has an annular shape as mentioned above, such pressure variation is propagated in the circumferential direction of the suction chamber, causing pressure pulsation in the suction chamber.
In some cases the pressure pulsation is notably amplified in a specific frequency range which depends on the size of the suction chamber, that is, the circumferential length of the suction chamber. Such amplified pressure pulsation not only causes vibrations of the components of the refrigeration circuit, such as a suction pipe connected to the suction port of the suction chamber and the evaporator connected to the suction pipe, but also increases noise from the components. Specifically, in the case of compressors of sizes used in automotive air conditioning systems, the pressure pulsation is liable to be amplified especially in the frequency range around 500 Hz.
To reduce the vibrations and noise, a muffler may be inserted in the suction pipe or an expansion chamber communicating with the suction chamber may be formed in the cylinder head. However, the use of the muffler leads to increase in the number of components of the refrigeration circuit, and also it is not easy to secure space for the muffler in the engine compartment of the vehicle. Forming the expansion chamber, on the other hand, leads to increased size of the cylinder head and thus of the compressor, also making the arrangement of the compressor in the engine compartment difficult.